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Where Medicare Advantage is most popular

States in the Midwest, South and West have the highest proportions of Medicare members enrolled in Medicare Advantage. Some states have more than 40% of their Medicare population in the taxpayer-subsidized private plans.

The big picture: Roughly a third of all Medicare enrollees are in MA, a program that has garnered bipartisan support despite its shortcomings, and some Wall Street estimates think MA will be the majority option by 2021.

By the numbers: More than 22 million seniors and people with disabilities have a Medicare Advantage plan, according to February 2019 enrollment data from the Centers for Medicare & Medicaid Services. The map highlights enrollment data from 2017, when there were 19.2 million MA enrollees.

The state with the highest proportion of private Medicare plan enrollees (57.3%) is Minnesota, although many people are enrolled in "Medicare cost" plans that function as a hybrid between MA and traditional Medicare.

MA is the choice of at least 40% of all Medicare enrollees in 6 other states (California, Florida, Hawaii, Oregon, Pennsylvania and Rhode Island).

MA is far less popular in states with sparse populations, like Alaska, Vermont and Wyoming.

Between the lines: States with high concentrations of MA enrollees also have dominant systems of hospitals and doctors that sell MA plans.

Many MA members in Pennsylvania buy plans from Highmark, Geisinger and UPMC, while Kaiser Permanente has a strong grip of the market along the West Coast.

What to watch: Health insurance companies will always aggressively pursue areas where there are a lot of seniors, like Florida and California, but the distribution shows there are pockets of the Midwest and Northeast that could be their next targets.